LED streetlights contributing to UK moth declines

A ground-breaking new study from Butterfly Conservation, the UK Centre for Ecology & Hydrology and Newcastle University has shown how streetlights in southern England reduce the abundance of moth caterpillars.

In the first study to demonstrate major, long-term and real-world negative impacts of light pollution on moth populations, the findings showed that caterpillar abundance declined by up to half (47% reduction in hedgerows and 33% reduction in grass margins) in areas lit by LED streetlights. Artificial light was also found to impact the development of caterpillars, as well as the feeding behaviour of nocturnal caterpillars.

Surveying for moth caterpillars under LED streetlights (Douglas Boyes).

The study also demonstrated that negative impacts were more pronounced under the supposedly 'eco-friendly' white LED streetlights compared to conventional yellow sodium lamps, indicating that the ongoing shift to use of white LEDs to illuminate roads, walkways and other human environments will have substantial consequences for insect populations and ecosystem processes.

The researchers believe that street lights might deter moths from laying their eggs, while also putting them at greater risk of predation from bats and other species.

Long-term moth declines have been reported from parts of Europe, especially in Britain (thanks to its long history of monitoring). In Britain, moth numbers have declined by one third since the 1970s. There are also sporadic data showing evidence of moth declines in other parts of the world.

The silver lining is that this is in theory an easily resolvable issue. Douglas Boyes, lead author of the study, explained: "Solving other biodiversity threats like climate change often means long delays between taking action and seeing the benefits. But when it comes to light pollution, there are no such lag effects between action and outcome. If lights are switched off – or at least dimmed during the early hours – darkness returns immediately. Our wildlife would be expected to recover quickly."

Read a fuller article by Douglas Boyes on his findings and their potential ramifications here.